Blister copper produced in converters or direct to blister furnaces must be purified of sulfur and oxygen before it can be cast to anodes. This is done in anode furnaces (AF) in a process known as fire refining.
Typically fire refining of blister copper is performed in two phases, oxidation phase and reduction phase. In oxidation phase air is blown to the blister copper and oxygen comprised in the air oxidizes sulfur to gaseous sulfur dioxide. Some of the oxygen also dissolves in the molten blister copper at the oxidation phase. The dissolved oxygen is removed in a reduction phase where a reductant, such as natural gas, is blown in the oxidized blister copper.
In order to achieve good quality anode copper for anode casting, sulfur concentration of the blister copper must be decreased to below 50 ppm. However, for achieving the required sulfur concentration a rapid increase of dissolved oxygen in the blister copper is induced at the end of the oxidation phase. This leads to copper losses to slag and to prolonged reduction phase causing high reductant consumption.
CN101314819B proposes a one phase fire refining process, wherein argon, industrial nitrogen, saturated steam or mixture thereof is blown in the copper and oxidation and reduction phases are omitted.